Thermal indicator for electrical apparatus



Feb. 19, 1963 R. E. ROOD THERMAL INDl'CATOR FOR ELECTRICAL APPARATUS me@ Feb. 1s. 1959 4Sheets-Sheet l 4 25 M www@ i. lllllllllil\ INVENTOR Robert E. Rood M fa ATTORNEY MQ?. MCM

eo 's2 WITNESSES ww Feb. 19, 1963 R- E ROOD THERMAL INDICATOR FOR ELECTRICAL APPARATUS Filed Feb. 15, 1959 4 Sheets-Sheet 2 Fig 3 Feb. 19, 1963 R. E. ROOD 3,077,776

THERMAL INDICATOR FOR ELECTRICAL APPARATUS Filed Feb. 15, 1959 4 Sheets-Sheet 3 Fig.6.

Feb. 19, 1963 R. E. ROOD THERMAL INDICATOR FOR ELECTRICAL APPARATUS 4 Sheets-Sheet 4 Filed Feb. 13, 1959 United States Patent O 3,677,776 THERMAL ENDQTR iFl'l ELEC'ERECAL AHAPATUS Robert E. Rood, Sharon, Pa., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. l5, 1959, Ser. No. 793,@26 ll7 Claims. (Si. l-356D This invention relates to thermal indicators for electrical apparatus such as transformers.

In certain types of conventional electrical apparatus, such as transformers, it has been the common practice in building such appmatus to bury thermostats, thermocouples and other thermally responsive devices in the windings or coils of such apparatus, the temperature or thermal load condition of which it is desired to measure or indicate. If such thermal indicating equipment should require repair, it may be necessary to tear down the windings or other parts of such apparatus. The latter procedure may also be necessary to add thermal indicating equipment to existing electrical apparatus.

ln copending application Serial No. 793,027, tiled February 13, 1959, by Herbert W. Book and assigned to the same assignee as the present yapp ication, there is disclosed an improved thermal or temperature indicator which does not require thermally responsive parts or devices to be built into the windings or coils or the associated electrical apparatus and which is particularly adapted for installation external to, or on the outside of the casing or housing of electrical apparatus of the enclosed type. While the thermal indicator disclosed in said copending application is suitable for most applications, therc are certain applications where it is required to provide an indicator which shows that the associated electrical apparatus is eing or has `been subjected to a thermal load in excess of a predetermined value. It is, therefore, desirable to provide a thermal or temperature indicator for electrical apparatus which has all of the advantages of the indicator disclosed in said copending application and which has several additional advantages in certain applications.

lt is an object of this invention to provide for indicating the thermal load condition ot an electrical apparatus.

lt is also an object of this invention to provide for indicating the temperature of an electrical apparatus.

Another object of this invention is to provide for measuring and indicating the temperature or thermal load condition of an electrical winding or coil which is so disposed in a casing or relative to other apparatus that it is not readily accessible.

A further object of this invention is to provide means for indicating the thermal load condition of electrical apparatus which responds to a magnetic field resulting from the flow of electrical current which causes the heating of said apparatus.

A still further object of the invention is to provide a thermal indicator for electrical apparatus of the enclosed type which is particularly adapted for installation external to or on the outside of the casing of such apparatus.

A more speciilc object oi the invention is to provide for indicating when the thermal load condition of an enclosed electrical apparatus exceeds a predetermined value.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the followf ing detailed description taken in connection with the accompanying drawings, in which:

FlGURlE 1 is a iront View, in elevation, ot a thermal indicator illustrating a iirst embodiment of the invention;

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FlG. 2 is a top plan View, in section, of the indicator shown in HG. l;

HG. 3 is a partial front sectional View, in elevation, of the indicator shown in FlG. l;

FlG. 4 is a side elevational View, partially in section, of the indicator shown in FlG. l;

yFll. 5 is a front view in elevation of a thermal indicator illustrating a second embodiment of the invention;

FlG. 6 is a top plan view, partially in section, of the indicator shown in FlG. 5;

FlG. 7 is a partial side elevational View, in section of the indicator shown in PEG. 5;

FIG. 8 is a perspective view illustrating an alternative form or" the magnetic member included in the indicators shown in FlGS. 2 and 6; and

FIG. 9 is a partial View in elevation illustrating the manner in which the indicators shown in FIGS. l through 4 or in FIGS. 5 through 7, respectively, would be mounted on the associated electrical apparatus.

Referring nonl to the drawings and FIGS. 1 through 4 and 9 in particular, there is shown in general a temperature or thermal load indicator l@ illustrating a iirst embodiment of the invention. he indicator for electrical apparatus shown generally at lll is a modiiication suitable for application to a distribution transformer. rihe casing or housing of the associated electrical apparatus, such as a transformer, is indicated at .''ttlk in FIG. 9. The electrical apparatus enclosed or disposed inside the casing Soil: may be a transformer core and coil assembly (not shown) to and from which electrical current is carried from outside of the casing fido by associated leads which may include one or more conductors, such as the conductor 53d, having a covering of insulation thereon, as shown in FlG. 9. 'l` he conductor 53d may be connected to a suitable terminal connector 522 and the electrical current carried by the conductor 53u may pass through the casing or housing tltl through a suitable bushing 52d as shown in FlG. 9.

The ilovv or electrical current to the associated electrical apparatus through one or more of the conductor leads 55d causes the temperature or thermal load condition f the electrical windings or coils of the associated apparatus inside the casing Soil to change, the extent of such changes being measured and indicated by the thermal indicator The thermal indicator lli, as illustrated, is particularly adapted to indicate when the temperature or thermal load or the associated electrical apparatus eX- yeeds a predetermined value. Since the thermal indicator ltr is disposed adjacent to the leads of the assocated electrical apparatus, it is preferable that, if the indicator lid is employed with a transformer core and coil assembly, the indicator lll should be disposed adjacent to the secondary or low voltage leads associated with said assembly in order to reduce the insulation requirements in the construction of said indicator.

As best shown in FIG. 9, the thermal indicator lil is mounted or secured on the outside of the casing Edil of the associated electrical apparatus by any suitable means, such as the stud member Sli-.Z which is Welded or otherwise secured to the casing Silo and a bracket member l, which in turn is secured to said stud member and the thermal indicator llt). Referring particularly to FlC-S. l, 4 and 9, the thermal indicator ld comprises an indicating case or housing 2G and a base member 3d which may be both molded or cast from a suitable material, such as a silicone rubber or elastomer, that will have adequate strength and capacity to resist the Weather when mounted outdoors. Since the indicator lil may be associated with a transformer which is mounted on poles or in some location well above the ground level, the indicating case 2t, the base member 3d and the bracket member l'tl may be arranged so that the indicating case ft-d of tie indicator f, sa

itl will be inclined at an angle to the horizontal to facilitate observation from the ground.

The thermal indicator lt) also includes means for sensing the temperature of the associated electrical apparatus inside the casing Elli): rl'he sensing means comprises a magnetic member lll@ which is mounted or disposed inside the base member or housing 3d as shown in FlGS. 1, 2 and 3. Both the base member 3l? and the magnetic member lili include two openings or apertures 3.22 and 11.2, respectively, which permit one or more leads, such as the conductor lead 53d shown in FIG. 9, to pass through said base member and said magnetic member. As best shown in FIG. 3, the magnetic member llt? may be conveniently formed from two plates or sheets 114, each of said plates including a curved portion between the apertures llrZ to form a cavity or receptacle as indicated at 125. As explained in copending application Serial No. 649,116, tiled by Herbert W. Book and assigned to the same assignee as the present application for a magnetic member of the same general type, the magnetic member lltl is preferably formed from a metallic magnetic material and may be molded from powdered metals or cast in one piece from metallic material or formed in other suitable ways that are well known in the art and that will provide the features to be described here` inafter. The size, shape and thickness of the magnetic member llt) will depend to a large extent on the apparatus with which it is to be employed. The selection o the magnetic material from which the magnetic member lli) is formed may also depend on the thermal insulation to be employed with said member and may be formed from any o the well-known magneticmetals, alloys or metallic oxides which are available.

As explained in the copending application just mentioned, whenever electrical current flows through the conductor leads 536 to an associated electrical apparatus inside the casting Still, a magnetic lield willbe set up adjacent to or around the conductor leads 53u shown in FIG. 9. rl`he density of the magnetic iield set up around the conductor leads 530 will vary with the magnitude or amount of the current flowing in said leads. When a metallic magnetic member, such as the member llt), is disposed in a magnetic field around one or more of the conductor leads 530, many of the lines of magnetic liuX in the space around said member will be concentrated in it to thereby heat up said member. The member lill thus accumulates heat which varies with the density of the magnetic flux around oneY or more of the conductor leads 530, which in turn varies with the electrical current flowing in said leads and in the associated electrical apparatus inside the casing 509. Since the temperature or thermal load condition of the electrical apparatus, which may include electrical windings or coils inside the casing Stili, also varies with the current ilowing in the leads 530, thel temperature or thermal condition of the magnetic member il@ will vary as a function of the temperature or thermal condition of the apparatus inside the casing Slltl. In other words, the magnetic member liti may be suitably designed to provide a thermal image of the electrical apparatus which is disposed inside the casing Stltl.

The base member Sil comprises a cover member 32 and a lower portion 34. The cover member 32 includes a groove or narrow recess which extends around the periphery on the underside of said cover member. The lower portion 34 of the base member 36 includes a projecting portion 184 which substantially lilis the groove 186 of the cover member 32 when said cover member and said lower portion are assembled. The groove 13a may be at least partially lled or coated with a suitable thermosetting resin, such as an epoxy resin, prior to the assembly of the cover member 32 with the lower portion 3d in order to secure said cover member to said lower portion and to seal the joint between said parts of the base member 36. T he cover member 32 is also provided with two cylindrical projecting members lSS which may be formed integrally with the cover member 32 to form the apertures' 122 through which one or more of the leads 53o may pass. rlhe lower portion 34 of the base member 3@ is also provided with two cylindrical projecting members i9@ which iit over the outside of the cylindrical members M of the cover member 32 when the cover member 3?. and said lower portion are assembled as shown in FlG. 3. As shown in FIG. 3, the magnetic member' llt) may be supported between the cylindrical members 1194 of the lower portion S-t of the base member 39' and the shoulder or ledge portions 192 on the cylindrical members 195 of the cover member 32.

ln order to control the heat transfer from the magnetic member litt, the base member 3* is preferably formed from a thermally insulating material which may also be an electrically insulating material to assist in insulating the magnetic member lll from the conductor leads 53d. The thermal insulation 15b may also be disposed around at least a portion of the magnetic member il@ to assist in the control of heat transfer from said member. The thermal insulation lStl may be provided in the form of polyester glass, wool or matting or as a cast member which assists in supporting the magnetic member llt?. lt is to be understood that in certain applications, a portion of the base member 3% may be formed from thermally conducting .material to more closely create a thermal image or reilection having similar thermal characteristics to the electrical apparatus inside the casing or housing Still. ln other words, by proper selection and design ot the base member 3@ and the thermal insulation l5@ as well as the magnetic member lill, the temperature or thermal condition of the magnetic member lill may more closely correspond to the thermal operating characteristics ot the associated electrical apparatus.

ln order to supply electric power to indicating means included in the thermal indicator lil', which will be described hereinafter, a iirst terminal or external ground strap 132 is secured to the base member lill by suitable means such as the rivet 134, which is best shown in FIG. 1. A suitable conductor or internal ground strap 136 having one end connected to the rivet 134 and having the other end secured to the magnetic member lill by suitable means, such as brazing or welding, connects the tirst terminal 132 to the magnetic member 116. A second terminal or line terminal 142 is secured to the base member 3l? by the rivets 144, as shown in FIGS. 1, 2 and 4. ln order to limit the voltage applied to the associated indicating means when a source of electric power is connected between the terminals 132; and 142, a suitable are shield or gap protector 160 is disposed adjacent to the second terminal 142. The gap protector i60 comprises a cylindrical member formed from a suitable insulating material, such as porcelain, a lirst electrode secured to the terminal lll?. and a second electrode i541. The second electrode 15'4- of the protector ll?` is secured to the base member 30 by the rivet 155 which in turn is connected to the magnetic member lltlby the conductor strap 152, which is secured to the magnetic member by suitable means, such as brazing or welding. lt is to be noted that the base member Si? is secured to the bracket member 170, as best shown in FIG. 2, by any suitable means such as the -bolts 64 and the associated nuts 368 and the lock washers 166. ln order to provide a seal where the bolts ldd pass through the openings in the base member 39, the gaskets or O-ring packing members 156 may be provided around said bolts.

In order to sense the temperature or thermal condition of the magnetic member lili), which is a function of the temperature of the associated electrical apparatus as previously mentioned, a thermally responsive device or means, more specifically a helical bimetallic element 120, which may be of any conventional type, is disposed in the receptacle 32S. In orderrto improve the response of the bimetal rZtl to the temperature or thermal condition of aoc/7,7715

the magnetic member llt?, the axes of the receptacle L and the bimetallic element F.2d lie in substantially the same plane as the magnetic member il. l and said bimetal is preferably surrounded by said magnetic member. ln order to provide a smooth surface for the receptacle 125 in which the bimctal lill may rotate as it detorms in respouse to or is actuated by the temperature of the magnetic member illu, a sleeve or tube member lili is disposed insid-e the receptacle llZi as best shown in FGS. 2 and 3. The tube member ll is preferably formed from a material having a high degree of thermal conductivity and preferably one of a non-corrosive type, such as copper or brass. ln order to adjust the response of the bimetallic element l2@ to the temperature or thermal condition of the magnetic member il@ or to cornpensate for different environmental ambient temperatures, a bimetal adjusting knob ldd is secured to one end oi the bimetallic element l2@ by any `suitable means, such as bonding with an epoxy resin. In order to prevent axial movement or the birnetal adjusting knob ist@ while still permitting said knob to be rotated, said knob is provided with a circular groove or recess lai in which is disposed a retaining ring 172 at the point Where said knob passes into the inside of the base member 39. A spring type lock washer le@ is disposed around the adjusting knob lid-tl to assist in preventing axial movement of said knob and is disposed where said knob passes throngl the bracket member in order to provide a seal Where the adiustiug knob passes through the base member 3ft, a suita le gasket or G-ring packing member ld is provided or disposed around said knob at the point where the adjusting knob le@ leaves the outside of the base member Fill. ln order `to complete an electrical circuit which will be described hereinafter, a leaf spring type contact may be electrically connected to the helical bimetallic element l2@ at the point where said bimetal is secured to the adjusting knob idf-5 and arranged to rotate with said knob in contact with the inside surface of the tube member 124i. The latter arrangement is based on providing an adjusting knob l/iil formed from electrically insulating material. lAlternatively, the adjusting knob liit may be formed `lrom an electri ily conducting material in electrical contact with the bnnetallic element lit@ and the leal spring Contact llfzfl omitted.

ln order to indicate tie temperature or thermal condition ci the magnetic member llt?, a rotatable shaft 13% is secured or attached to tre helical bimetal i2@ by suitable means, such as soldering or brazing. As the electrical current which flows in the lead conductors 5Std changes, the magnetic linx around said leads changes and the temperature of the magnetic member il@ changes. rhe helical bimetallic element l2@ responds to, or actuated by changes in the temperature ot the magnetic member to cause the rotatable shaft i3d to turn in one direction or the other depending upon the change in the te irerature of the magnetic member lili.

in order to provide a visual indication of the temperature or thermal condition of the magnetic member il@ when the temperature or thermal condition of the magnetic member liti and the increasing temperature or thermal load condition of the associated electrical apparatus inside the casing ddd exceeds a predetermined value, contact means are coupled or disposed to be responsive to the temperature or thermal condition of the magnetic member Zilli as sensed by the helical bi .ietaliic element 12th in general, when the temperature of the magnetic member il@ and the corresponding temperature or thermal load condition of the associated electrical apparatus exceeds a predetermined value, the contact means, which is disposed in the indicating case or housing Ztl and which cooperates or is actuated by the helical bimetallic element Mtl, is arranged to energize or change the energization of an indicating device or means, more specifically, the signalling lamp or light Sil which is also disposed inside the indicating case Ztl.

In particular, a Contact arm Gti having a moving contact el mounted or disposed thereon is connected or attached to the rotatable shaft F.3d, as best shown in FIGS. l and 2. The contact arm d@ is preferably formed from an electrically conducting material for reasons which will be explained hereinafter. The contact arm di?, as shown in illG. l, is arranged to rotate as the rotatable shaft rotates in response to changes in the temperatures of the magnetic member liti, as sensed by the helical bimetallic element llZti, which actuates said rotatable shaft. A stationary contact d2 is disposed in the path of the contact arm titl as it rotates in a clockwise direction, the stationary contact 62 being preferably formed from a material which has permanent magnetic properties. The stationary contact 62 is secured to a bracket member 5?. by suitable means, such as the rivet '64. The bracket member 52 is secured in turn to the indicating case Ztl by the rivets 54 which also assist in securing the indicating case 2d to the base member 3d', as best shown in FlGS. 2 and 4.

The indicating lamp titl which is preferably of the neon glow type, is supported by a bracket member 5S which is secured to the indicating case 2d by the rivet 56 and by the supporting member de which may be formed integrally with the indicating case Ztl as a projecting part on the inside ot said indicating case, as best shown in FlGS. l and 4. ln order to increase the visibility oi the indicating lamp dil when energized and viewed from the ground or any distant location, a reilecting member which may be of the polished metal type, is disposed between the lamp dll and the supporting member Sd, said supporting member having a suitable curved recess in which said refleeting member may be attached or otherwise secured. it should be noted also that the rivet 56 which secures the bracket member dil to the indicating case Ztl and assists in securing said indicating case to the base member 3@ is electrically connected to the second terminal M2 by the conductor left, as best shown in FiG. 4.

ln order to complete the electric circuit which ener gizes the lamp dit, one terminal of the lamp 8i? is conne l ted to a current limiting resistor ed through a con doctor 'l2 and the other terminal of the lamp d@ is connected through a conductor 82 to the bracket member 5S which is preferably formed from electrically conducting material. The other side of the current limiting resistor de is connected through the conductor dit to the bracket member 52 which is also preferably formed from electrically conducting material. The current limiting resistor tid may be supported inside the indicating case Ztl by any suitable means such as the supporting member 7d, which in turn is secured to the indicating case 2d. In order to clamp the conductors 82 and ed to the bracket members S3 and 52 respectively and to insure a good electrical connection between said conductors and said bracket members, a generally tJ-shaped clamping member 65, which is preferably formed from an electrically insulating material, is disposed to hold the conductors 82 and 63 in position. The clamping member dS is secured in turn by suitable means such as the screw or rivet '76 which engages a projecting supporting member 67 which is preferably formed integrally with the indicating case Ztl. It is to be noted that the material from which the indicating case 2@ is termed must be electrically insulating as well as weatherproof for a purpose which will be discussed hereinafter.

ln order to protect the parts of the indicator lill, which are disposed inside the indicating case 2t?, a suitable window made from a transparent material, such as glass or a suitable plastic material, is secured to the front end of the indicating case Ztl by a metallic bezel ring 94 which clamps the window @2; to the flanged portion 96 of the indicating case Ztl. ln order to seal the indicating case 2d, a gasket 9S is disposed between the window 92 and the langed portion @d of the indicating case 2d. In order to seal the joint between the base member Si) and the amarre indicating case 2d, which are secured to each other by the rivets and d6, a suitable gasket or O-ring packing member l'd is disposed in a suitable recess in said base member at the point where the indicating case Zh* and the base member are in contact with each other.

lit is to be noted that the stationary contact which is preferably formed as a permanent magnet operates to latch or hold the moving contact which is disposed on and rotates with the contact arm di? in the closed position, after the temperature of the magnetic member il@ and the corresponding temperature of the associated ele trical apparatus has exceeded a predetermined value. In order to provide means for resetting the contact arm d@ after it has reached the position shown in PEG. l and is being held in the position shown in FlG. l by the permanent magnet from which the stationary contact is formed, a resetting member is disposed adjacent to the contact arm when it is in the closed position. rThe resetting member l2 includes a projecting part d3 which passes through and extends below the indicating case 2d, as shown FlG. l. in order to maintain the resetting member in the position shown in FIG. l, a biasing spring '73 is disposed between said resetting men-- ber and the bracket member 52. The biasing spring 78 may be positioned by the projecting part @d on the bracket member 52 and the projecting part t6 on the resetting member 42. The resetting member 4Z also includes a projecting arm 44 which moves up to lift the Contact arm 6i) oit the stationary Contact 62 when the projecting part d3 of the resetting member d2 is pushed upward against the biasing spring 7d. When pressure is removed from the projecting part i3 of the resetting member 42, said resetting member is returned to the position shown in FIG. 1 by the biasing spring 78. In order to seal the opening in the indicating case 2d where the resetting member 42 passes through said indicating case, a suitable gasket or O-ring packing member is disposed adjacent to the inside of said indicating case where the resetting member d?. passes through said indicating case.

The over-all operation of the thermal indicator lil will now be considered. Referring to FlGS. l, 3 and 9, when current flows in one or more or" the conductor leads 53? to and from the electrical apparatus inside the casing 509 to thereby cause said apparatus to heat up, the temperature of the magnetic member il@ will vary with the temperature or thermal load condition of the associated electrical apparatus inside the casing Stili. The helical bimetallic element lid is then actuated by the change in the temperature ot the magnetic member ll@ to thereby cause the rotatable shaft i3d which in turn causes a corresponding rotation of the contact arm ed, as shown in FlG. l. As the temperature o the magnetic member il@ and the corresponding temperature of the associated electrical apparatus increases, the contact arm 6@ will rotate in a clockwise direction until the moving contact el disposed thereon comes into Contact with or into a closed position with the stationary contact 62. Assuming that the terminals 132 and Irl-@12 are connected to a source of electrical power or current, the lamp d@ will be energized when the contacts 6l and 63 are in a closed position, as shown in FIG. l. The electrical circuit which energizes the lamp {it} may be traced starting from terminal .1132, then through the rivet 134 the internal conductor strap i3d to the magnetic member lid, the to the tube member through the leaf spring contact lili to the helical bimetallic element lfi, then through the rotatable shaft i3@ to the contact arm ab, through the moving contact di to tue stationary contact 62, then through the bracket member 52, through the conductor titi, the current lim ing resistor 6d and the conductor 72 to one terminal of the lamp Sil. The other terminal of the lamp titl is connected to the terminal W through the conductor 82, the bracket member 53, the rivet and the conductor 82, as best shown in FiG. 4. The encrgization of the lamp ist), after the thermal load of t' e assoi ciated electrical apparatus has exceeded a predetermined value, is maintained by the stationary contact d2 which functions as a latching or holding means to keep the contacts di and in the closed position, as shown in FG. l and as previously discussed.

lt is to be understood that the terminals E132 and 142 of the thermal indicator lo may be conveniently connected to the associated electrical apparatus to provide a source of electrical current or power to energize the lamp 86. For esaple, it the associated electrical apparatus inside the casing or tank Sd, shown in FIG. 9, is a transformer, the terminal i3?. could be conveniently connected to a ground terminal on the casing 56d and the terminal 142 could be conveniently connected to the terminal connector 522 on the low voltage or secondary bushing 52d, as shown in FIG. 9. Since certain types of electrical apparatus are subject to surge voltages, the gap protector or arc shield Teti, shown in FGS. l and 2, would operate to limit the voltage applied to the thermal indicator ld to a safe value in order to prevent damage to said indicator. in other words, the electrodes 54 and 148 of the gap protector le@ are arranged to break down at substantially a predetermined value and limit the voltage applied to the thermal indicator it! Whenever a predetermined surge voltage is present between the terminals l32 and M2.

Referring now to FlGS. 5 through 7, there is illustrated a thermal load indicator 2% which is similar to the thermal indicator lil, except that the thermal indicator 26S also includes means for indicating che thermal load condition of the associated electrical apparatus at any given time, as well as indicating when said apparatus is being or has been subjected to a thermal load in excess of a predetermined value. ln addition, the thermal indicator Ziltl, as illustrated, includes means for indicating the maximum thermal load of the associated electrical apparatus between successive readings of said indicator.

In particular, the thermal indicator 200 comprises a base member 3G which is identical to the base member 30 of the thermal indicator 1d, except with respect to several minor details which will be discussed hereinafter, and an indicating case 22% which is similar to the indicating case 2d of the thermal indicator lli?, except for the type of indicating means which is disposed inside the indicating case 22d. The parts of the base member 30 which are identical to the equivalent parts of the base member 3h bear the same reference numerals.

The indicating case E20 is secured to the base member 3d by the rivets 273 and 277 and is preferably formed from the same type of material as previously described for the indicating case Ztl of the thermal indicator It). For reasons which will be discussed hereinafter, the rivet 2273 is electrically connected to the magnetic member il@ by the conductor 275 and the rivet 277 is electrically connected to the second terminal 142 through one of the rivets ldd and the conductor 279. The base member 3d', except as just noted, is otherwise identical to the `base member Si? previously described for the thermal indicator ld. Similarly to the indicating case 2t), the i11- dicating case 22d includes a window 292 which is secured to the hanged portion 29d of the indicating case 220 by the bezel ring 294 and is sealed by the gasket 298.

ln order to provide a visual indication of the temperature of tl e magnetic member lit), an indicating hand pointer 2,96 is attached to the rotatable shaft 13d and disposed in front or" a dial member 24th, shown in FIGS. 5 and 6. The dial member Zdti is disposed inside the indicating case '22@ and may be supported by any suitable means such as the supporting members 225 which may be formed integrally with the indicating case 220 and the screws 2M which pass through the dial member 246 and engage the supporting members 225'.

Since the temperature of the magnetic member 1li? varies with the temperature or thermal load condition of the associated electrical apparatus inside the casing bdd, .he dial member 25rd may be calibrated in terms of the ther-mal load of the associated apparatus, which may include windings or coils. In particular, the dial member 2d@ may be calibrated to indicate the percentage of the rated thermal load of the associated electrical apparatus. The deection or location of the indicating hand pointer 29d provides a visual indication of the thermal load condition or temperature of the associated electrical apparatus. In order to indicate the maximum thermal load of the associated electrical apparatus between isuccessive readings, a maximum indicating hand pointer is movably disposed about the axis of the rotatable shaft 13G in any suitable manner. As illustrated, a supporting member 254 may lbe attached to the indicating case 22d at the point where the shaft 130 passes through said indicating case and the maximum indicating hand pointer 27d` rotatably mounted or disposed on the supporting member 254. The `supporting member 254 may also assist in supporting the shaft 13d as said shaft Vpasses into the indicating case 220 as indicated at 259.

Since the maximum indicating hand pointer 279 is disposed between the indicating hand pointer 290 and the dial member 24d, the maximum hand pointer 276 may be provided with a projection or cam member 272 which is arranged to lbe driven or rotated by the indicating hand pointer 29d to the highest or maximum point of travel or deiiection of the hand pointer 294) during the operation of the indicator 20d. Suitable means may also be provided for retaining the maximum indicating hand pointer in the highest point or position to which it is driven by the hand pointer, such as the spring 213 which still permits the maximum indicating hand pointer 27@ to be driven or rotated by the hand pointer 2%. Since the indicating hand pointer 2%- is arranged to drive the maximum indicating hand pointer 270 only in the upward or clockwise direction, the maximum indicating hand pointer 27d remains at the maximum point of travel or dei'iection of the indicating hand pointer 2% whenever the bimetallic element i2@ cools and causes the indica'ting hand pointer 29d to rotate in a counterciockwise direction to a lower thermal load reading.

In order to provide a visual indication when the thermal load of the associated electrical apparatus is presently exceeding or has exceeded a predetermined value, Contact means are provided in the indicating case for energizing or changing the energization of an indicating device or means, more speciically an indicating iight or lamp 22d which i-s preferably of the neon glow type. Ey suitable selection of the connections of the indica-usar 2id?, the indicating lamp 2S@ lmay be energized wherever the thermal load ot the associate-d electrical apparatus is presently in excess of a predetermined value by the operation of contacts associated with the indicating hand pointer Alternatively, the indicating lamp may be energized and maintained in an energized condition to indicate that the thermal load of associated electrical apparatus 'has exceeded a predetermined value between successive readings or during a particular period since the resetting of the maximum hand pointer 27d virile the associated electrical apparatus has been in operation.

in particular, a moving contact 27S is disposed or mounted on the indicating hand pointer 29d and rotates with said indicating hand pointer. A stationary contact 255, which is generally C-shaped as shown in HG. 5, is

mounted on the hanged portion 255 of the supporting member The moving contact 278 on the indicating hand pointer 2% is arranged to slidably engage the stationary contact 253 when the thermal load of the associated electrical apparatus exceeds a predetermined value such as the thermal load indicated by the numeral 2 on the dial member 24d which may correspond to or indicate 209% of the rated thermal load of the associated electrical apparatus. When the moving contact 278, which may be formed integrally from the indicating hand pointer 2% and which may be of the spring type or brush type contact, engages the stationary contact 253, the lamp 280 is energized 'from the source of electric current which is connected between the terminals 132 and M2 of the base member 30. The electrical circuit which energizes the lamp 2S@ may be traced from the terminal B2, through the .rivet 134, the conductor strap 136, the magnetic member 11d, the tube member T24, the leaf spring contact 121, the bimetallic element 12d, the shaft 130, the indicating hand pointer 2M, the moving contact 278, the stationary Contact 253, through the conductor 233 to the terminal 243v and through the conductor 245 to one terminal of the lamp 2&1?. The other terminal of the lamp 230 is connected to the terminal 142 through the conductor 239, the current limiting resistor 266, the conductor 26S, the rivet 277, the conductor 279 and through the rivet 144 to the terminal 142. The indicating lamp 23d and the current limiting resistor 266 may be suitably supported inside the indicating casing 22d by the supporting members 28d and 257, respectively, which are in turn secured to said indicating case. It is important to note that the electrical circuit just described for energizing the lamp 23d is completed .by the moving cont-act 278 yon the indicating hand pointer 29@ only when the indicating hand pointer indicates a thermal load in excess of a predetermined value. When the indicating hand pointer 2% rotates to a lower thermal load position below said predetermined value, the above circuit is interrupted since the moving contact 278 no longer engages the stationary contact 253 and the above circuit is interrupted to deenergize the indicating lamp 2de. in other words, when the conductor 24S connects one terminal of the lamp 28d` to the terminal 243 the indicating lamp is operated in essentially an ono manner.

Alternatively, the indicator 2% may be connected to have the indicating lamp 23@ controlled by the operation of the maximum hand pointer 27d. This may be accomplished yby connecting one terminal of the indicating lamp 23d by the conductor 2-/i7 to the terminal 241, which in turn is connected to the stationary contact 252. The stationary contact 252 is similar to the stationary contact 253 and is mounted on the back of the hanged portion 255 of the supporting member 254:, as shown in FIGS. 6 and 7. A moving contact 26S is disposed or mounted on the maximum hand pointer 270 and rotates with said maximum hand pointer. The moving Contact 26S may also be formed integraily with the maximum hand pointer 270 and may be of the spring type or brush type to Slidably engage the stationary contact 252 whenever the position of the maximum hand pointer 27dy is above a predetermined thermal load reading on the dial member 246. The position at which the moving contact 26S slidably engages the stationary contact 252 may be the same or at a diiierent position as for the indicating hand pointer 29d. Whenever the indicating hand pointer 2%" drives the maximum hand pointer 27) above a predetermined position or when the corresponding thermal load of the associated electrical apparatus exceeds a predetermined value, the contacts associated with the maximum hand pointer 27d slidably engage to close an electrical circuit which cnergizes the indicating lamp from the source or" electrical current connected between the terminals 132 and M2. The electrical circuit which energizes the indicating lamp 23@ in the latter case may be traced from the terminal 232, through the rivet i3d, the conductor strap 136, the magnetic member 110, the conductor 275, the rivet 273, the conductor 262 which electrically connectsthe rivet 273 and the spring 2id, the spring 218, the maximum indicating hand pointer 270, the moving contact 26S, the stationary Contact 252, the conductor 23, the terminal 241 and the conductor 247 to one terminal of the lamp 280. The other terminal of the lamp 28th is completed through the electrical circuit,

ypreviously described, to the terminal 142 to thereby energize the lamp 284). The' contacts 268 and 252 which are closed by the movement or rotation of lthe maximum indicating hand pointer 270, therefore, energize the indicating lamp 28@ when the thermal load of the associated electrical apparatus exceeds a predetermined value and said maximum hand pointer is driven by the indicating hand pointer 29@ to ya position which closes said contacts. Since the contacts 268 and 252 associated with the indicating hand pointer then remain closed independently of the position of the indicating hand pointer when the associated electrical apparatus cools down and the indicating hand pointer 290 rotates in a counterclockwise direction, said contacts provide a holding circuit yfor maintaining the energization of the indication lamp 280, similarly lto the stationary contact 62 of the thermal indicator which was preferably formed as a permanent magnet. It is thereby noted that for proper operation of the electrical circuits just described for energizing the lamp 280, the supporting member 254 on which the stationary contacts 252 and 253 are mounted and the dial member 240 must be formed from an electrically insulating material.

In summary, the mode of operation of the indicator 200 with respect to the energization of the lamp 280 is determined by connecting one terminal of the lamp 280 to either the terminal 241 or to the terminal 243 by either the conductor 247 or the conductor 245, respectively. The selection of the latter connection determines whether the energization of the indicating lamp 280 is control-led by the contacts associated with the indicating hand pointer 290 or by the contacts associated with the maximum hand pointer 270, as just discussed. When the energization of the lamp 280 is controlled by the movement of the indicating hand pointer 290, said indicating lamp is only energized when the indicating hand pointer 290 is at a position which indicates that the thermal load of the `associated electrical apparatus is presently in excess of a predetermined value. When the associated apparatus cools and the thermal load decreases below said predetermined value, the indicating lamp 280 is then deenergized by the counterclockwise rotation of the indicating hand pointer 290. On the other hand, if the energization of the indicating lamp 280 is controlled by the rotation of the maximum hand pointer 270 which is driven bythe hand pointer 290, the indicating lamp 280 is energized when the maximum hand pointer 270 is driven by the hand pointer 290 to a position which indicates that the thermal load of the associated electrical apparatus has exceeded a predetermined value and the llamp then remains energized independently of the position of the indicating hand pointer 290 until the maximum hand pointer 29() is reset by suitable means (not shown), such as an external magnetic device. It is to be understood that the alternative connections of the indicating lamp 280 to the contacts associated with either the indicating hand pointer 290 or the maximum hand pointer 270 may be accomplished by a suitable selector switch rather than by the changes in -the connections of one of the Vterminals of said lamp to one of the terminals 241 or 243.

it is to -be noted that the contacts associated with the hand pointers 290 and 270 are each equivalent to a rotary switch whose position is controlled by the movement or' said hand pointers, and it is to be understood that conventional rotary switches could be substituted for the contact means associated with either of the indicator hands 270 and 290. It is to be noted that the mounting of the indicator 200 on the associated electrical apparatus could be provided similarly to that of the indicator 1t), as shown in FlG. 9, with the indicator 200 substituted for the indicator 10.

Considering the over-all operation of the thermal load or temperature indicator Zitti, the temperatur-e or thermal load condition of the associated electrical apparatus in- The changes in the electrical current through the conductor leads 536) also causes a corresponding change in the temperature of the magnetic member 1l() which is a function of and varies with the temperature of the associated electrical apparatus inside the casing 500. A change in the temperature or thermal condition of the magnetic member 1l@ causes the helical bimetallic element l2@ to be actuated in response to said changes in temperature which in turn causes a turning movement of the rotating shaft 130. The rotation of the shaft 130 causes a change in the deflection of the indicating hand pointer 290 which causes -a change in the thermal load reading on the calibrated dial member 240 of the indicator 260. The maximum travel or dellection of the indicating hand pointer 299 between successive readings is indicated visually by the position of the maximum indicating hand pointer 279, as previously discussed. It is to be understood that the dial member 24u may also be calibrated in terms of various other conductors associated with an electrical apparatus which varies with the electrical current owing to and from said apparatus. lFinally, as previously discussed, the indicating lamp 289 provides an indication of Whether the thermal load of an associated electrical apparatus is presently exceeding a predetermined value or alternatively has exceeded said predetermined Value since the maximum hand pointer 290 was previously reset to a position which corresponds to a value below said predetermined value. It is to be understood that in a particular application, only one of the latter modes of operation may Ibe provided in a thermal indicator similar to the thermal indicator 200.

tis to be understood that the magnetic member lill may be provided in different sizes and shapes in different applications, but Vit is essential that the magnetic member be disposed in the magnetic field of the leads in which electrical current ows to and from associated electrical apparatus whose thermal condition depends on the amount of electrical current ow in said apparatus. Referring to FIG. 8, there is illustrated an alternative form of the magnetic member 110 which is particularly adapted for installation around the leads of an associated electrical apparatus without disturbing said leads since said leads are not required to pass through holes in the magnetic member 410, shown in FIG. 8. In particular, the magnetic member 410 is similar to the magnetic member 110 since it is formed from two plates 41.4 each having a curved portion near the middle of the said .plates to form a cavity 425 in which a thermally responsive device such as a helical bimetallic element may be disposed. Each of the plates 414 which comprises the magnetic member 410 includes a generally U-shaped recess, as indicated at 422, which permits the mounting of the magnetic member 410 around the leads of an associated electrical apparatus such as the leads 530, shown in FlG. 9, without disturbing said leads. It is to ybe understood that in an indicator which includes the magnetic member 41% rather than the magnetic member lit) that the base member surrounding the magnetic member 410 would have to Ibe suitably modified to also include recesses which would correspond to the recesses 422 included in the magnetic member 410.

Although it is preferred to have the magnetic member, such as the magnetic member 110, included in an indicator of the type disclosed, substantially surrounded by thermally insulating materials as described for the indicators llt) and Zitti, it may be desirable in certain applications to provide thermally conductive material adjacent to a portion of said magnetic member to function as a heat sink in order to have the magnetic member more closely simulate the thermal operating characteristics or qualities of an associated electrical apparatus. lt is also desirable that the magnetic member 110 and the thermally insulating material employed to control the heat transfer from said member .be designed so that the thermal time constant of said member more closely ap- 13 proaches the thermal time constant of the associated electrical apparatus.

It is also to be understood that other types of signalling devices, such as audible alarms may be substituted for the signal lamps S and 236 in the indicators 16 and Zitti, respectively.

The apparatus embodying the teachings of this invention has several advantages. For example, the thermal load indicator or temperature indicator, as disclosed, may be readily mounted or installed on existing electrical apparatus of the enclosed type without the necessity for opening the casing of said apparatus. In addition, the thermal image of an electrical apparatus made availble outside the casing of said apparatus is eiectively employed in a thermal indicator which either may indicate whether the associated apparatus is presently exceeding or has exceeded a predetermined value of thermal load and may also indicate the present thermal load of the associated apparatus in terms of a percentage of the rated thermal load of said apparatus.

Since numerous changes maybe made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawing, shall be interpreted as illustrative and not in a limiting sense.k i

I claim as my invention:

l. A thermal load indicator for electrical apparatus including an electrical winding inside a casing which is subject to heating when conducting electrical current and leads connected to said winding for conducting current to and from said winding, the current flow through said leads setting up a magnetic field around said leads, comprising a magnetic member disposed in said eld outside said casing which causes said member to heat up when current flows in said leads, said magnetic member including one or more conductor passages through which said leads may pass, a bimetallic element disposed adjacent to said member for deforming in response to the temperature of said member, a base member for enclosing said magnetic member, said base member being formed from a thermally insulating material and including a cover member having one or more openings and having extending portions around each of said openings which pass through the conductor passages of said magnetic member, and indicating means associated with said bimetallic element -for indicating when the thermal load of said apparatus exceeds a predetermined value as said bimetal deforma.

2. A thermal load indicator for a transformer having an electrical coil disposed in a casing which heats up when carrying electric current and leads connected to saidcoil for supplying electric current thereto, the current flow through said leads setting up a magnetic iield around said leads, comprising a magnetic member disposed outside said casing in said eld to heat up when current flows in said'leads, said magnetic member comprising two plates each having tirst and second apertures assembled in substantial registry to form a receptacle therebetween, the temperature of said member varying with that of said coil, a helical bimetallic element disposed in the receptacle of said member for deforming in response to the temperature of said member, contact means coupled to said bimetallic element to be actuated when the thermal load of said transformer exceeds a predetermined value, a base member for enclosing said magnetic member, said base member being formed from a thermally insulating material and including a cover member having one or more openings and having extending portions around each of said openings which pass through the apertures of said magnetic member, and indicating means responsive to the actuation of said contact means for indicating when the thermal load of said transformer exceeds said predetermined value.

3. A thermal load indicato-r for a transformer having an electrical coil in a casing which heats up when carrying electric current and leads connected to said coil for supplying electric current thereto, the current ilow through said leads setting up a magnetic field around said leads, comprising a magnetic member disposed outside said casing in said iield to heat up when current iiows in said leads, said magnetic member comprising two assembled plates shaped to provide a receptacle therebetween and provided with one or more openings through which one or more leads may pass, the temperature of said member varying with that of said coil, a helical bimetallic element disposed in the receptacle of said mem-ber for detorming in response to the temperature of said member, a rotatable shaft connected to said bimetallic element Contact means coupled through said shaft to said bimetallic element to be actuated when the thermal load of said transformer exceeds a predetermined value, and a signal light responsive to the actuation of said contact means through a circuit which includes said magnetic member, said bimetallic element and said shaft connected in series circuit relation for indicating when the thermal load of said transformer exceeds said predetermined value.

4. A thermal load indicator for a transformer having an electrical winding in a casing which heats up when carrying electric current and leads connected to said winding for carrying current to and from said Winding, the iiow of current causing a magnetic held around said leads, comprising a magnetic member disposed outside said casing in the tield o at least one of said leads, the temerature of said member varying with that of said winding, a bimetallic element disposed adjacent to said member for deforming in response to the temperature of said member, a rotatable shaft connected to said bimetallic element, a contact arm having a moving contact disposed thereon, said arm being disposed on said shaft, a stationary contact disposed in the path of said contact arm, said contacts being arranged to close when the thermal load of said transformer exceeds a predetermined value, and signalling means connected in series c"cuit relation with said bimetallic element, said shaft, said contacts and said magnetic member to be energized therethrough when said thermal load exceeds said predetermined value.

5. A thermal load indicator for a transformer having an electrical winding in a casing which heats up when carrying electric current and leads connected to said winding for carrying current to and from said winding, the iiow of current causing a magnetic iield around said leads, comprising a magnetic member disposed outside said casing in the field of at least one of said leads, the temperature of said member varying with that of said winding, a bimetallic element disposed adjacent to said member for deforming in response to the temperature or" said member, a rotatable shaft connected to said bimetallic element, a contact arm having a moving contact disposed thereon, said arm being disposed on said shaft', a stationary contact disposed in the path of said contact arm, said contacts being arranged to close when the thermal load of said transformer exceeds a predetermined value, signalling means connected in circuit relation with said contacts to be energized when said thermal load exceeds said predetermined value, the energizing circuit of said signalling means including said magnetic member, said bimetaliic element and said shaft connected in series circuit relation and holding means for maintaining said contacts in the closed position after said thermal load exceeds said predetermined value independently of the position of said contact arm,

6. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding which heats up when carrying electric current and leads connected to said winding for carrying current to and from said winding, the flow of current causing a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of at least one of said leads, said magnetic member comprising two as sembled plates having one or more apertures through which one or more leads may pass, the temperature of said member varying with that or" said winding, a helical bimetallic element disposed adjacent to said member for deforrning in response to the temperature of said member, a casing of thermally insulating material for enclosing said member and said bimetallic element to control the heat transfer from said member, the latter casing including a cover member having one or more openings and extending portions around said openings which pass through each of said apertures of said magnetic member, a rotatable shaft connected to said bimetal, a contact arm having a moving Contact disposed thereon, said arm 4being disposed on said shaft, a stationary Contact disposed in the path of said contact arm, said contacts being arranged to close when the thermal load of said transformer exceeds a predetermined value, and signalling means connected in circuit relation with said contacts to be energized when said thermal load exceeds said predetermined value independently of the position of said Contact arm.

7. A thermal load indicator for a transformer having an electrical winding in a casing which heats up when carrying electric current and leads connected to said winding for carrying current to and from said winding, the liow of current causing a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of at least one of said leads, said magnetic member comprising two plates assembled to provide a receptacle therebetween, the temperature of said member varying with that of said winding, a helical bimetallic element disposed in the receptacle of said member for deforming in response to the temperature of said member, a rotatable shaft connected to said bimetallic element, a contact arm having a moving contact disposed thereon, said contact arm being disposed on said shaft, a stationary contact disposed in the path of said contact arm, said contacts being arranged to close when the thermal load of said transformer exceeds a predetermined value, signalling means connected in circuit relation with said contacts to be energized when said thermal load exceeds said predetermined value, the energizing circuit of said signalling means including said magnetic member, said bimetallic element and said shaft connected in series circuit relation and holding means for maintaining said contacts in closed relation and for maintaining the energization of said signalling means after said thermal load exceeds said predetermined value independently of the position of said contact arm.

8. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding which heats up when carrying electric current and leads connected to said winding for carrying current to and from said winding, the flow of current causing a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of at least one of said leads, the temperature of said member varying with that of said winding, a helical bimetallic element disposed adjacent to said member for deforming in response to the temperature of said member, a rotatable shaft connected to said bimetallic element, a contact arm having a moving contact disposed thereon, said arm being disposed on said shaft, a stationary contact disposed in the path of said contact arm, said contacts being arranged to close when the thermal load of said transformer exceeds a predetermined value, signalling means connected in circuit relation with said contacts to be energized when said thermal load exceeds said predetermined value, the energizing circuit of said signalling means including said magnetic member, said bimetallic element and said shaft connected in series circuit relation and holding means for maintaining said contacts in closed id relation and for maintaining the energization of said signalling means after said thermal load exceeds said predetermined value, independently of the subsequent thermal load of said transformer, said holding means comprising a permanent magnet disposed adjacent to said stationary Contact.

9. A thermal load indicator for a transformer having an electrical winding in a casing subject to heating when carrying electric current and leads for carrying current to and from said winding, the iiow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current fiows in at least one of said leads, the temperature of said member varying with that of said winding, a helical bimetallic element disposed adjacent to said member to deform in response to the temperature of said member, a rotatable shaft connected to said bimetailic element indicating means actuated by said bimetallic element through said shaft for indicating the thermal load of said transformer, and a signalling means Venergized by said indicating means through a circuit which includes said magnetic member, said bimetallic element and said shaft electrically connected in series circuit relation when the thermal load of said transformer exceeds a predetermined value.

l0. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding subject to heating when carrying electric current and leads for carrying current to and from said winding, the fiow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current flows in at least one of said leads, said magnetic members including one or more conductor passages through which said leads pass the temperature of said member varying with that of said winding, a helical bimetallic element disposed adjacent to said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, a base member for enclosing said magnetic member, said base member being formed from a thermally insulating material and including a cover member having one or more openings and having extending portions around each of said openings which pass through the conductor passages of said magnetic member, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value.

11. A thermal load indicator for a transformer having an electrical winding in a casing subject to heating when carrying electric current and leads for carrying current to and from said winding, the flow of vcurrent through said leads creatinga magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when Current flows in at least one of said leads, the temperature of said member varying with that of said winding, a helical bi'- metsllic element disposed adjacent tov said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimettallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value, said signalling means comprising a moving contact disposed on said indicating hand pointer and a stationary contact disposed adjacent to said indicating hand to be slidabiy engaged by said moving Contact when the thermal load of said transformer exceeds a predetermined value, and

17 a signal light connected in series circuit relation with said bimetallic element, said shaft, said contacts and said magnetic member to be energized when said thermal load exceeds said predetermined value.

l2. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding subject to heating when carrying electric current and leads for carrying current to and from said winding, the flow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current ows in at least one of said leads, said magnetic member having two plates each having first and second conducto-r passages through which said leads may pass, said plates being shaped and assembled in substantial registry to form a receptacle therebetween, the temperature of said member varying with that of said winding, a helical bimetallic element disposed in the receptacle of said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, and a follower hand pointer disposed about said shaft to be driven by said indicating hand pointer to indicate the maximum indication of said indicating hand pointer, a base member for enclosing said magnetic member, said base member being formed from a thermally insulating material and including a cover member having one or more openings and having extending portions around each of said openings which pass through the conductor passages of said magnetic member, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value.

13. A thermal load indicator for a transformer having an electrical winding in a casing subject to heating when carrying electric current and leads for carrying current to and from said winding, the ow of current through said leads creating a magnetic field around said leads, Comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current flows in at least one of said leads, the temperature of Said member varying with that of said winding, a helical bimetallic element disposed adjacent to said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, and a follower hand pointer disposed about said shaft to be driven by said indicating hand pointer to indicate the maximum indication of said indicating hand pointer, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value, said signalling means comprising a rotary switch having a moving contact disposed on said follower hand pointer and a stationary contact disposed adjacent to said follower hand pointer to be slidably engaged by said moving contact when the thermal load o-f said transformer exceeds a predetermined value, and a signalling lamp connected in series circuit relation with said follower hand pointer, said magnetic members and said contacts to be energized when said contacts are engaged by the movement of said follower hand pointer, said lamp being then energized independently of the position of said indicating hand pointer.

14. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding subject to heating when carrying electric current and leads for carrying current to and from said winding, the flow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current liows in at least one of said leads, the

temperature of said member varying with that of said Winding, a helical bimetallic element disposed adjacent to said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of Said hand pointer, and a follower hand pointer disposed about said shaft to be driven by said indicating hand pointer to indicate the maximum indication of said indicating hand pointer, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value, said signalling means comprising contact means actuated by said follower hand pointer when said thermal load exceeds said predetermined value and a signal lamp connected in series circuit relation with said magnetic member, said follower hand pointer and said contact means to be energized independently of the position of said indicating hand pointer after said contact means are actuated.

l5. A thermal load indicator for a transformer having an electrical winding in a casing subject to heating when carrying electric current and leads for carrying current to and from said winding, the flow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the field of said leads to heat up when current flows in at least one of said leads, said magnetic member comprising two assembled plates having one or more openings through which one or more leads may pass, the temperature of said member varying with that of said winding, a helical bimetallic element dispose adjacent to said member to deform in response to the temperature of said member, a casing of thermally insulating material for enclosing said member and said bimetal to control the heat transfer from said member and match the thermal characteristics of said member with those of said transformer, said latter casing including a cover member having one or more apertures and extending portions around each of said apertures which pass through said openings indicating means for indicat- .ing the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, and a follower hand pointer disposed about said shaft to be driven by said indicating hand pointer to indicate the maximum indication of said indicating hand pointer, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value, said signalling means comprising contact means actuated by said follower hand pointer when said thermal load exceeds said predetermined value and a signal lamp connected in series circuit relation with said follower hand pointer, said magnetic member and said contact means to be controlled independently of the position of said indicating hand pointer after said contact means are actuated.

16. A thermal load indicator for a transformer having an electrical winding subject to heating when carrying electric current and leads for carrying current to and from said winding, the flow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed in the field of said leads to heat up when current flows in at least one of said leads, said magnetic member comprising two plates shaped and assembled to form a receptacle therebetween, the temperature of said member varying with that of said winding, a helical bimetallic element disposed in the receptacle of said member to deform in response to the temperature of said member, indicating means for indicating the temperature of said member, said indicating means comprising a rotatable shaft connected to said bimetallic element, an indicating hand pointer attached to said shaft, and a dial member disposed back of said hand pointer, and signalling means actuated by said indicating means when the thermal load of said transformer exceeds a predetermined value, said signalling means comprising a rotary switch actuated by the movement of said indicating hand, said switch hand having a moving contact `disposed on said indicating hand pointer and a stationary contact disposed adjacent to said indicating hand to be slidably engaged by said moving contact when the thermal load of said transformer exceeds a predetermined value, and a signal light connected in series circuit relation with said contacts to be energized through said magnetic member, said bimetallic element and said shaft When said ther mal load exceeds said predetermined value.

17. A thermal load indicator for mounting outside the casing of a transformer having an electrical winding subject to heating when carrying electric current and leads for carrying current to and from said winding, the ow of current through said leads creating a magnetic field around said leads, comprising a magnetic member disposed outside said casing in the eld of said leads to heat up when current ows in at least rone of said leads, said magnetic member comprising two assembled plates having one or more openings through which one or more leads may pass, the temperature of said member varying with that of said winding, a helical bimetallic element disposed adjacent to said member to deform in respo-nse to the temperature of said member, a rotatable shaft connected to said bimetallic element thermal insulation disposed around said member and said bimetallic element to control the heat transfer from said member so that the thermal time constant of said member approaches that of said transformer, indicating means actuated by said bimetallic element through said shaft for indicating the thermal load of said transformer, and a signalling means energized by said indicating means through a series circuit which includes said bimetallic element, said magnetic member and said shaft when the thermal load of said transformer exceeds a predetermined value.

References Cited in the tile of this patent UNITED STATES PATENTS 747,297 Bristol Dec. 15, 1903 1,020,045 Merryman Mar. 12, 1912 1,463,189 Baker July 31, 1923 1,470,079 Hoeschen Oct. 9, 1923 1,485,013 Blakeslee Feb. 26, 1924 1,917,163 Stephens et al. July 4, 1933 1,953,914 Camilli Apr. 3, 1934 2,456,062 Iwanski Dec. 14, 1948 2,468,693 Stoecklin et al Apr. 26, 1949 2,502,159 Lamb et al. Mar, 28, 1950 2,680,214 Ford June 1, 1954 2,722,679 Barr Nov. 1, 1955 FOREIGN PATENTS 487,735 Great Britain June 24, 1938 571,125 Great Britain Aug. 8, 1945 

1. A THERMAL LOAD INDICATOR FOR ELECTRICAL APPARATUS INCLUDING AN ELECTRICAL WINDING INSIDE A CASING WHICH IS SUBJECT TO HEATING WHEN CONDUCTING ELECTRICAL CURRENT AND LEADS CONNECTED TO SAID WINDING FOR CONDUCTING CURRENT TO AND FROM SAID WINDING, THE CURRENT FLOW THROUGH SAID LEADS SETTING UP A MAGNETIC FIELD AROUND SAID LEADS, COMPRISING A MAGNETIC MEMBER DISPOSED IN SAID FIELD OUTSIDE SAID CASING WHICH CAUSES SAID MEMBER TO HEAT UP WHEN CURRENT FLOWS IN SAID LEADS, SAID MAGNETIC MEMBER INCLUDING ONE OR MORE CONDUCTOR PASSAGES THROUGH WHICH SAID LEADS MAY PASS, A BIMETALLIC ELEMENT DISPOSED ADJACENT TO SAID MEMBER FOR DEFORMING IN RESPONSE TO THE TEMPERATURE OF SAID MEMBER, A BASE MEMBER FOR ENCLOSING SAID MAGNETIC MEMBER, SAID BASE MEMBER BEING FORMED FROM A THERMALLY INSULATING MATERIAL AND INCLUDING A COVER MEMBER HAVING ONE OR MORE OPENINGS AND HAVING EXTENDING PORTIONS AROUND EACH OF SAID OPENINGS WHICH PASS THROUGH THE CONDUCTOR PASSAGES OF SAID MAGNETIC MEMBER, AND INDICATING MEANS ASSOCIATED WITH SAID BIMETALLIC ELEMENT FOR INDICATING WHEN THE THERMAL LOAD OF SAID APPARATUS EXCEEDS A PREDETERMINED VALUE AS SAID BIMETAL DEFORMS. 